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Do parents favor their biological children over their adopted ones?

Wicked stepmothers would seem to be favored by evolutionary theory. The best way to ensure the propagation of our own genes, after all, is to take care of children who are genetically related to us—not those born to other parents. To see how this so-called kin selection theory might apply to adoptive parents, researchers compared data on 135 pairs of “virtual twins”—siblings about the same age consisting of either one adopted child and one biological child or two adopted children. In general, parents did not favor a biological child over an adopted one in all instances, the team reports online in Evolution and Human Behavior. Although parents did rate their adoptive children higher in negative traits and behaviors like arrogance and stealing, they scored both adopted and biological children similarly when it came to positive traits like conscientiousness and persistence. In modern times, the rise of private domestic and international adopting in the United States has made it much easier for parents to adopt. Such evolutionarily novel circumstances, the researchers argue, are creating conditions where the strong desire to be a parent—no matter the source of a child’s genes—can override evolved, kin selection behaviors that might otherwise lead parents to invest more time and resources in their own offspring.